Re: ddb(4) spoils kernel stack in CURRENT?

I've identified the workaround code in DDB. I'll commit a fix as soon as I
have some time to test my changes.

              -Kip

On 12/20/06, Kip Macy <kip.macy_at_gmail.com> wrote:
>
> I worried that gdb probably had workaround for the large stack argument.
> I'll have to dig it up, thanks for the heads up.
>
>   -Kip
>
> On 12/20/06, Dmitry Pryanishnikov <dmitry_at_atlantis.dp.ua> wrote:
> >
> >
> > Hello!
> >
> > On Wed, 20 Dec 2006, Kostik Belousov wrote:
> > >>> So it looks like a regression in CURRENT vs RELENG_6 (either ddb
> > 'spoils'
> > >>> the stack somehow, or kgdb fails to unwind it).
> > >
> > > Could you further localize the problem, i.e. try to backtrace CURRENT
> > dump
> >
> >    Good news: I've managed to localize the bug! I'm Feeling Lucky (TM)
> > ;)
> > just because CURRENT on my notebook was updated approx. at 17-Dec 00:00,
> >
> > and it didn't manifest such a behaviour! So it was easy to identify the
> > regression - it comes with the following commit:
> >
> > -----------------------------------------------------------------------
> >
> > Date: Sun, 17 Dec 2006 05:07:01 +0000 (UTC)
> > From: Kip Macy <kmacy_at_freebsd.org>
> > To: src-committers_at_freebsd.org, cvs-src_at_freebsd.org ,
> > cvs-all_at_freebsd.org
> > Subject: cvs commit: src/sys/i386/i386 apic_vector.s exception.slocal_apic.c
> >           trap.c vm86.c vm86bios.s src/sys/i386/include apicvar.h
> >           src/sys/i386/isa atpic.c atpic_vector.s icu.h
> >
> > kmacy       2006-12-17 05:07:01 UTC
> >
> >    FreeBSD src repository
> >
> >    Modified files:
> >      sys/i386/i386        apic_vector.s exception.s local_apic.c
> >                            trap.c vm86.c vm86bios.s
> >      sys/i386/include     apicvar.h
> >      sys/i386/isa         atpic.c atpic_vector.s icu.h
> >    Log:
> >    Evidently FreeBSD has long relied on the compiler to treat structures
> >    passed by value (trap frames) as if they were in fact being passed by
> >
> >    reference. For better or worse, this incorrect behaviour is no longer
> >    present in gcc 4.1. In this patch I convert all trapframe arguments
> > to
> >    be explicitly pass by reference. I also remove vm86_initflags,
> > pushing
> >    the very little work that it actually does up into vm86_prepcall.
> >
> > -----------------------------------------------------------------------
> >
> > So kernel built from sources as of date=2006.12.17.05.00.00 gives dump
> > with analyzable backtrace, and kernel built from sources as of
> > date=2006.12.17.05.10.00 (which include this commit) gives dump
> > which confuses kgdb. I believe that commit itself is correct,
> > but kgdb contains some workaround against the old (incorrect) behaviour
> > of the kernel, so it's the kgdb that should be fixed.
> >
> > Sincerely, Dmitry
> > --
> > Atlantis ISP, System Administrator
> > e-mail:  dmitry_at_atlantis.dp.ua
> > nic-hdl: LYNX-RIPE
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> >
>
>